'That's all I had TIME for,' said Henry, 'so that's the end of the presentation. Thanks for taking the TIME to listen.'

The other members of the village's Science Discussion Group, packed into the back room of the Cherry Tree pub, applauded at length. Henry gave a slight bow, switched off the projector and unplugged it from the laptop.

'That was an excellent presentation,' said Victoria. 'It must have taken you a lot of, er, TIME to prepare it.' General chuckles. 'We've got TIME for a couple of questions. Anyone?'

'Did you come across anything about time travel while you were researching the talk?' asked the retired doctor, sitting at the back.

'I did,' Henry said, 'but mainly in references to science fiction stories. The real scientists seem to agree that it's not possible.'

'Why's that?' asked the physicist. 'Isn't it the case that all the key equations in physics are symmetrical between time going forwards and time going backwards?'

Henry nodded. 'Yes, that's true. If you look at those equations alone, you can't find any reason why we couldn't travel in time. But—'

'It's cause and effect,' said the historian. 'Cause has to come before whatever it is that happens as a result of the cause. You can't have effect and then cause. If you had time travel, we could, er, pick up that spoon over there before Alf dropped it.' Alf looked down with surprise.

'Could you? Not sure about that,' Henry said. 'Anyway, the philosophers of science argue that cause and effect are just a human construct. They're our way of making sense of the world. They don't really exist.'

'Typical bloody philosophers,' muttered the chemist. 'I'd like to see one punch my fist with his nose.'

'Actually,' Henry said, 'I think you can forget the problem of the physics equations being symmetrical between the past and the future. There are good reasons why time travel is impossible.' He looked at Victoria and raised an eyebrow.

'Go on,' she said, looking at the clock on the mantlepiece. 'We've got a few more minutes.'

'Right. If you drop an egg on the floor, the result is a mess. A smashed egg. Suppose I showed a video of that.' He gestured at the screen behind him. 'And then I showed it going backwards, from the smashed egg to the whole one. It would be obvious which was with time going forwards and which was time going backwards.'

'So are you saying the physics is wrong?' asked the lawyer. 'The equations thing?'

'I'm saying the equations aren't the whole picture.'

Henry looked round the room.

'Lots of puzzled faces. Ok, here's another reason. Logic. The grandmother paradox. If I could travel back in time, I could accidentally kill my grandmother before she gave birth to my mother, and so I wouldn't exist. And so I couldn't travel back in time to kill her, so I would exist. Et cetera.'

'That's pretty convincing,' said the lawyer.

Murmurs of agreement.

'Anyway,' said the chemist, 'if people could travel back in time, we'd see the results now – we'd be using inventions that could only happen in the future, for example. And we don't see that.'

'Excellent point on which to end,' Victoria said. 'Many thanks to Henry. A very interesting session.' She stood up. 'Let's wrap it up now. See you all next month, same time, same place.'

She picked up the laptop while Henry slid the projector into its case. Chairs scraped as the group stood, donned their coats, and straggled out of the pub's back door. Some stood chatting in the yard while others waved their goodbyes and disappeared round the corner into the main street.

Victoria carried the laptop and projector over to the coach house. 'I'm going into town,' she called. 'Anyone want a lift?'

She climbed into her carriage and the ostler handed her the reins.